Ink level sensing

ABSTRACT

Ink reservoirs containing binary elements facilitate discrete sensing of ink level within the reservoir. The binary elements are adapted to provide an electrical path in response to an applied electrical signal if the element is immersed in the ink. The binary elements are further adapted to present an open circuit in response to the same applied electrical signal if the element is above a level of the ink. The binary elements may be single-use or multi-use elements, i.e., their state change may be irreversible or reversible, respectively. Based on the presence or absence of an electrical path, the ink level can be deemed to be at or above a level of the binary element, or below the level of the binary element, respectively.

FIELD OF THE INVENTION

[0001] The present invention relates generally to sensing of ink levelwithin an ink reservoir for use in a printing system.

BACKGROUND

[0002] A variety of printing systems, e.g., printers, copiers, facsimile(fax) machines and multifunction devices, utilize ink as a markingmaterial. The ink is contained in ink reservoirs often referred to ascartridges. The ink is a liquid, and often an aqueous liquid.

[0003] As the printing system deposits the ink on print media, the levelof ink in the cartridge will drop, eventually falling to a level whereink can no longer be delivered from the cartridge. At this point, thecartridge is deemed to be “empty” even though there is generally somequantity of ink retained in the cartridge.

[0004] It is generally advantageous to know when an ink cartridge isclose to being empty in order to give a consumer or other end user anopportunity to purchase a fresh cartridge. Additionally, operation of aprinter with a depleted ink supply may lead to loss of importantinformation. For example, a printing system printing a facsimile messagemay receive the transmitted information and operate as if the receivedinformation is being printed. If the ink is depleted, the information isnever printed. Unless the receiver can ask the sender to retransmit thefax, the information is irretrievable.

[0005] Knowing the relative ink level of the ink cartridge may beimportant under other considerations. For instance, before beginning alarge print job, it would be useful to know the likelihood that theremaining ink is sufficient to finish the print job. If the amount ofink is insufficient, the ink cartridge can be replaced or replenishedbefore it reaches its empty state in order to avoid wasting time, paper,and effort of unsuccessfully attempting to print the large print job.

[0006] For the reasons stated above, and for other reasons stated belowthat will become apparent to those skilled in the art upon reading andunderstanding the present specification, there is a need in the art foralternative methods and apparatus for indicating ink level within an inkreservoir for use in a printing system.

SUMMARY

[0007] Ink reservoirs containing binary elements are described herein tofacilitate discrete sensing of ink level within the reservoir. Thebinary elements are adapted to provide an electrical path, or closedcircuit, in response to an applied electrical signal if the element isimmersed in the ink. The binary elements are further adapted to presentan open circuit in response to the same applied electrical signal if theelement is above a level of the ink. The binary elements may besingle-use or multi-use elements, i.e., their state change may beirreversible or reversible, respectively. Based on the presence orabsence of an electrical path, the ink level can be deemed to be at orabove a level of the binary element, or below the level of the binaryelement, respectively.

[0008] Further embodiments of the invention include methods, apparatusand systems of varying scope.

DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1 is a perspective view of one exemplary embodiment of aprinting system in accordance with an embodiment of the invention.

[0010]FIG. 2 is a perspective view of an ink reservoir in accordancewith one embodiment of the invention.

[0011]FIG. 3 is a cross-sectional view of an ink reservoir in accordancewith one embodiment of the invention.

[0012]FIGS. 4A-4B are plan views of a binary element as a bimetal switchin accordance with one embodiment of the invention.

[0013]FIG. 5 shows signal traces of one embodiment of detecting inklevel in accordance with the invention.

[0014]FIG. 6 is a block schematic of a printing system coupled to a hostdevice in accordance with an embodiment of the invention.

[0015]FIG. 7 is a flowchart of a method of sensing ink level within anink reservoir in accordance with an embodiment of the invention.

DETAILED DESCRIPTION

[0016] In the following detailed description of the present embodiments,reference is made to the accompanying drawings that form a part hereof,and in which is shown by way of illustration specific embodiments inwhich the invention may be practiced. These embodiments are described insufficient detail to enable those skilled in the art to practice theinvention, and it is to be understood that other embodiments may beutilized and that process, electrical or mechanical changes may be madewithout departing from the scope of the present invention. The followingdetailed description is, therefore, not to be taken in a limiting sense,and the scope of the present invention is defined only by the appendedclaims and equivalents thereof.

[0017]FIG. 1 is a perspective view of one exemplary embodiment of aprinting system 10 shown with its cover open that includes at least onereplaceable ink reservoir 100 that is installed in a receiving station14. At least one of the replaceable ink reservoirs 100 is adapted toprovide an indication of ink level in accordance with an embodiment ofthe invention.

[0018] In operation, ink is provided from the replaceable ink reservoir100 to at least one inkjet printhead 155. The inkjet printhead 155 isresponsive to activation signals from a printer portion 18 to depositink on print media 22. The inkjet printhead 155 may be integral to thereplaceable ink reservoir 100 or the ink reservoir 100 may be removablyinstalled in the printing system 10 in flow communication with theprinthead 155. In either case, each ink reservoir 100 is in flowcommunication with its printhead 155.

[0019] For one embodiment, the replaceable ink reservoir 100, receivingstation 14, and inkjet printhead 155 are each part of a scanningcarriage that is moved relative to print media 22 to accomplishprinting. The printer portion 18 includes a media tray 24 for receivingthe print media 22. As the print media 22 is stepped through a printzone, the scanning carriage 20 moves the printhead 155 relative to theprint media 22. The printer portion 18 selectively activates theprinthead 155 to deposit ink on print media 22 to thereby accomplishprinting.

[0020] The scanning carriage 20 is moved through the print zone on ascanning mechanism that includes a slide rod 26 on which the scanningcarriage 20 slides as the scanning carriage 20 moves through a scanaxis. A positioning means (not shown) is used for precisely positioningthe scanning carriage 20. In addition, a paper advance mechanism (notshown) is used to step the print media 22 through the print zone as thescanning carriage 20 is moved along the scan axis. Electrical signalsare provided to the ink reservoir 100 for selectively activating theprinthead 155 by means of an electrical link such as a ribbon cable 28.Similarly, electrical signals are provided between the ink reservoir 100and the printing system 10 for the purpose of sensing ink level,preferably through the same electrical link. The various components formoving a printhead 155 relative to the print media 22, which may includemoving one or both of the printhead 155 and print media 22, may bereferred to as a printer engine.

[0021] It will be recognized that replaceable ink reservoirs 100, oftenreferred to as ink cartridges, may come in a variety of form factors andmay be usable in a variety of printing systems including, for example,printers, facsimile (fax) machines, copiers and multifunction devices.Similarly, the ink reservoirs 100 may contain a single ink color, e.g.,cyan, magenta, yellow or black, or they may be compartmentalized tocontain more than one ink color.

[0022]FIG. 2 is a perspective view of an ink reservoir 100 in accordancewith one embodiment of the invention. The ink reservoir 100 includes abody 105. A printhead 155 is integral to the body 105. The printhead 155includes ink ejectors 106 for dispensing ink onto a print media. The inkejectors 106 are controlled by various electrical signals received atone or more contacts 107. Some of the contacts 107 are further used todetect ink level within the body 105 as described with reference to FIG.3.

[0023]FIG. 3 is a cross-sectional view of an ink reservoir 100 inaccordance with one embodiment of the invention. The ink reservoir 100includes a body 105. The volume within the body 105 is adapted tocontain ink. The area enclosed by body 105 may represent thecross-section of a one-color ink reservoir or an individual chamber of amulti-color ink reservoir, with each chamber having its own binaryelements for detecting ink level. Thus, the various embodiments includeone-color and multi-color ink reservoirs.

[0024] The body 105 contains one or more binary elements, such as binaryelements 110 a and 110 b, for detection of ink level within the body105. The binary elements 110 a-b are any elements adapted to provide anelectrical path when the element is in an initial state and to presentan open circuit when the element is in a second state. For oneembodiment, the binary elements 110 a-b are fusible links. The conceptof fusible links, or fuses, is well known. Fusible links are conductivetraces, wires, strips and the like that provide an electrical path untilan excessive electrical signal is applied to the link. When anelectrical signal is applied to the fusible link having a current andduration exceeding the capacity of the fusible link, the conductivetrace, wire, strip or the like will heat up to the point of melting,thus severing the link and presenting an open circuit.

[0025] To apply the electrical signals, the binary elements 110 a-110 bare coupled to one or more electrical contacts 107 a-c. Additionalelectrical contacts, such as electrical contact 107 d, are utilized bythe printing system for such things as controlling ink ejectors of theprinthead 155.

[0026] Binary element 11 a is coupled to an electrical contact 107 athrough a lead 115 to receive an electrical signal as an appliedelectrical signal. The applied electrical signal will pass through thebinary element 110 a in its initial state and return on lead 120 tocontact 107 c. Binary element 110 b is coupled to an electrical contact107 b through a lead 125 to receive an electrical signal as an appliedelectrical signal. The applied electrical signal will pass through thebinary element 110 b in its initial state and return on lead 130 tocontact 107 c. Although the embodiment of FIG. 3 shows each binaryelement 110 a-b having its return signal coupled to an electricalcontact 107 c, each binary element 110 a and 110 b could have its returnlead 120 and 130, respectively, coupled to an individual electricalcontact 107.

[0027] The concept utilized herein is that a binary element 110 a-bimmersed in liquid, such as the ink, will have a higher electricalcapacity than a binary element 110 a -b exposed to air. This is due tothe significantly higher rate of heat transfer from the binary element110 a-b to a liquid versus air. Because heat is dissipated more quicklyin liquid, the binary elements 110 a-b can handle a higher currentbefore presenting an open circuit. If an electrical signal isperiodically applied to the binary elements 110 a-b that exceeds thecapacity of the binary elements 110 a-b if exposed to air, but is lessthan the capacity of the binary elements 110 a-b if immersed in the ink,it can be determined when the ink level falls below an individual binaryelement 110 a-b by monitoring for an open circuit in response to theelectrical signal. It is recognized that as the ink level passes by thebinary element, the binary element will, for a time, neither be totallyimmersed in ink or totally exposed to air. During this period, the heatdissipation characteristics will gradually change. Thus, the level ofthe binary element is that level where the binary element would beexpected to change state and present an open circuit in response to theelectrical signal regardless of whether the binary element is partiallyimmersed in ink.

[0028] The desired current and duration of the electrical signal is thatcurrent and duration that will not exceed the capacity of the binaryelement in ink, but will exceed the capacity of the binary element 110a-b in air. It is noted that the desired current and duration is a rangeof current and duration levels dependent upon the chosen materials andrelative heat transfer coefficients. For example, a binary element inair may be rated to carry 4A for 1 second or 8A for 0.2 seconds. Theinvention is not limited by any specific material choice as mostconductive materials can operate as a fusible link with their capacitybeing controlled generally by controlling the minimum cross-sectionalarea of the link. However, the material should be chosen based onexpected corrosion or other compatibility issues with the ink containedin the body 105 as the fusible link is preferably exposed directly tothe ink. By utilizing multiple binary elements 110 a-b at differentlevels within the body 105, the ink level can be monitored at varioususage levels.

[0029] Prior to operation, the ink reservoir 100 would be filled withink. Initially, the ink may have a level indicated by dashed line 140.At this initial level, each binary element 110 a-b is below a level ofthe ink and, therefore, immersed in the ink when the ink reservoir 100is installed in a printing system. Application of the electrical signalat the desired current and duration will not cause the binary elements100 a-b to present an open circuit. Because each of the binary elements110 a-b maintains an electrical path, it can be determined that the inklevel is above a level of the binary element 110 a, i.e., above thehighest binary element.

[0030] As ink continues to be expelled from the body 105, the ink willeventually fall to a level indicated by dashed line 145. At this level,a first binary element 110 a is above the level 145 of the ink and isthus exposed to air. Application of the electrical signal at the desiredcurrent and duration will cause the binary element 110 a to heat to thepoint that it presents an open circuit. However, a second binary element110 b is still below the level 145 of the ink and is thus totallyimmersed in liquid. Application of the electrical signal at the desiredcurrent and duration will not cause the binary element 110 b to heat tothe point that it presents an open circuit. Because the binary element110 a presents an open circuit and the binary element 110 b provides anelectrical path, it can be determined that the ink level isapproximately between a level of the binary element 110 a and the binaryelement 110 b.

[0031] As more ink is expelled from the body 105, the ink willeventually fall to a level indicated by dashed line 150. At this level,each binary element 110 a-b is above the level 150 of the ink and thusexposed to air. Application of the electrical signal at the desiredcurrent and duration will cause the binary element 110 b to heat to thepoint that it also presents an open circuit. Because the binary element110 b now also presents an open circuit, it can be determined that theink level is approximately below a level of the binary element 110 b.When the ink level is determined to be below a level of the lowestbinary element, the ink reservoir 100 may be deemed to be empty.Alternatively, a further estimation of usage may be made using suchindirect techniques as drop counting. Because the indirect estimationtechnique is started at a known level lower than the initial ink level,the indirect estimation technique can be generally more accurate than ifit is utilized during the entire life of the ink reservoir 100.

[0032]FIGS. 4A-4B are plan views of a binary element as a bimetal switch410. In FIG. 4A, the bimetal switch is in its initial state. The bimetalswitch 410 includes a bimetal element 430 coupled between a first lead415 and a second lead 420 and mounted on a substrate 405, such as a wallof the body 105. The leads 415 and 420 would be coupled to electricalcontacts 107 as described in the preceding paragraphs. The bimetalelement 430 includes a first metal layer 432 bonded to a second metallayer 434. The metal layers 432 and 434 have differing coefficients ofthermal expansion, with the first metal layer 432 having a lowercoefficient of thermal expansion. In this manner, as the bimetal element430 heats up, the first metal layer 432 will tend to expand less thanthe second metal layer 434, thus causing the bimetal element 430 to bendin a direction of the first metal layer 432. As shown in FIG. 4B, as thebimetal element 430 bends in the direction of the first metal layer 432,the bimetal element 430 will lift away from the lead 420, thuspresenting an open circuit. When the electrical signal is removed, thebimetal element 430 will cool down, thus restoring the electrical path.By utilizing a multi-use binary element, such as bimetal switch 410, theink reservoir could be refilled while still allowing for an indicationof ink level during subsequent use. In the case of a fusible link, theink reservoir would not provide the same functionality if it were to berefilled unless the fusible link were also replaced.

[0033] A variety of techniques could be utilized to determine when abinary element is presenting an open circuit. FIG. 5 shows signal tracesof one embodiment of detecting ink level in accordance with theinvention. Trace 501 represents an applied signal, such as might beapplied to electrical contact 107 a of FIG. 2. Trace 502 represents areturn signal, such as might be sensed at electrical contact 107 c ofFIG. 2. During a time when the binary element 110 a provides anelectrical path, the trace 502 would be expected to be substantiallyidentical to the trace 501. Although FIG. 5 shows the pulses of traces501 and 502 to be essentially identical, it is recognized that resistivelosses will cause some deterioration of the return signal.

[0034] As shown in FIG. 5, during the pulse of trace 501 beginning attime t5 and having a duration of t6-t5, the corresponding pulse of trace502 is cut short. This would be an indication that the binary element isnow presenting an open circuit as an electrical signal is being applied,but not returned. In addition to monitoring the return signal forvoltage or current, detecting an open circuit could also be accomplishedby monitoring voltage or current of the applied signal. For example,there will be no current draw of the applied signal if an open circuitis presented. Similarly, a constant current signal applied to a closedcircuit will see a finite drop in voltage that will not be seen whenapplied to an open circuit.

[0035] For one embodiment, the electrical signals are appliedperiodically to the binary elements, e.g., every 10 seconds, once perminute, once every 5 minutes, etc. Alternatively, the electrical signalsmay be applied continuously, although this will result in an unnecessarypower drain as the ink level within most ink reservoirs will not changerapidly even during heavy usage. The monitoring of ink level may beperformed in response to the printing system being on, or only while itis processing a print job.

[0036] If an open circuit is detected on the applied signal side of thecircuit, the return circuits of multiple binary elements may be coupledto a single contact while permitting simultaneous monitoring of eachbinary element, such as depicted in FIG. 4. To monitor for an opencircuit on the return side of the circuit using a single return contact,simultaneous monitoring of multiple binary elements would generallyrequire some means to identify which element is presenting an opencircuit. For one embodiment, each element could be designed to have adifferent current capacity, e.g., with a first element having a currentcapacity of 1x, a second element having a current capacity of 2 x and athird element having a current capacity of 4x, where x is some value ofcurrent. In this manner, by monitoring the current output on the returnside of the circuit, it can be determined which binary elements areproviding an electrical path and which are presenting an open circuit.For another embodiment, the electrical signals for the individual binaryelements could be applied sequentially to determine which of the binaryelements is presenting an open circuit while still permitting the use ofa single return contact. Alternatively, each binary element could have aseparate return contact. For yet another embodiment, the binary elementsmay have their inputs coupled together to receive a single appliedsignal while monitoring individual outputs to detect an open circuit.

[0037]FIG. 6 is a block schematic of a printing system 610 coupled to ahost device 611, such as a personal computer, network server or otherdevice external to the printing system 610, in accordance with anembodiment of the invention. The printing system 610 has a processor 602for interpreting and rendering image data into a printable image. Theprintable image is provided to a print engine 606 to produce a tangibleoutput image on a print media. The print engine 606 represents themechanical aspects of the printing system 610. The image data for use bythe processor 602 may be received via a communication port 603 from thehost device 611 or stored on a computer-usable media 604. Similarly, thecomputer-usable media 604 may store printable images for use directly bythe print engine 606 without further rendering by the processor 602. Theprinting system 610 can have more than one communication port 603. Forexample, the printing system 610 may have an IR (infrared) port and aUSB (universal serial bus) port for access by one or more host devices611.

[0038] The processor 602 is adapted to perform one or more methods ofthe various embodiments of the invention in response tocomputer-readable instructions. These computer-readable instructions maybe in the form of either software, firmware or hardware. In a hardwaresolution, the instructions are hard coded as part of a processor, e.g.,an application-specific integrated circuit (ASIC) chip. In a software orfirmware solution, the instructions are stored on a separatecomputer-usable media 604 for retrieval by the processor 602. Someexamples of computer-usable media include static or dynamic randomaccess memory (SRAM or DRAM), read-only memory (ROM),electrically-erasable programmable ROM (EEPROM or flash memory),magnetic media and optical media, whether fixed or removable. Mostcomputer applications are software solutions provided to the user onsome removable computer-usable media, such as a compact disc read-onlymemory (CD-ROM).

[0039] For one embodiment, the processor 602, in response to thecomputer-readable instructions, is adapted to apply an electrical signalto a binary element contained within the ink reservoir 100, determinewhether an electrical path is present through the binary element, andprovide an indication of ink level in response to whether an electricalpath is detected.

[0040]FIG. 7 is a flowchart of a method of sensing ink level within anink reservoir in accordance with an embodiment of the invention. At 705,an electrical signal is applied to a binary element within the inkreservoir. At 710, the electrical path through the binary element ischecked. If no electrical path is detected at 715, i.e., an open circuitis detected, it is deemed at 720 that the ink level is below a level ofthe binary element. If an electrical path is detected at 715, it isdeemed at 725 that the ink level is at or above a level of the binaryelement. The determination of ink level may be presented to a user ofthe printing system by any combination of audible or visual indications.For one embodiment, a tone may be sounded by the printing system whenthe ink level is deemed to be below the level of the binary element anda text message may be displayed on a control panel of the printingsystem, such as “Ink Level 25%.” Alternatively, or in addition, audibleand/or visual indications may be given to the user at the host device.For example, the printing system may direct the host device to sound atone, present a text message on its user interface and/or present agraphic showing an ink cartridge having an ink level corresponding tothe ink level of the sensed ink reservoir.

CONCLUSION

[0041] Ink reservoirs containing binary elements have been describedherein to facilitate discrete sensing of ink level within the reservoir.The binary elements are adapted to provide an electrical path inresponse to an applied electrical signal if the element is immersed inthe ink. The binary elements are further adapted to present an opencircuit in response to the same applied electrical signal if the elementis above a level of the ink. The binary elements may be single-use ormulti-use elements, i.e., their state change may be irreversible orreversible, respectively. Based on the presence or absence of anelectrical path, the ink level can be deemed to be at or above a levelof the binary element, or below the level of the binary element,respectively.

[0042] Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat any arrangement that is calculated to achieve the same purpose maybe substituted for the specific embodiments shown. Many adaptations ofthe invention will be apparent to those of ordinary skill in the art.Accordingly, this application is intended to cover any adaptations orvariations of the invention. It is manifestly intended that thisinvention be limited only by the following claims and equivalentsthereof.

1. An ink reservoir for use in a printing system, comprising: acompartment for containing ink; and a first binary element contained ata fixed level within the compartment; wherein the first binary elementis adapted to provide a closed electrical circuit in response to a firstelectrical signal applied to the first binary element while a liquidlevel within the compartment is above the first binary element; andwherein the first binary element is adapted to provide an openelectrical circuit in response to the first electrical signal applied tothe first binary element while the liquid level within the compartmentis below the first binary element.
 2. The ink reservoir of claim 1,further comprising: at least one additional binary element, wherein eachadditional binary element is contained at a fixed level within thecompartment; wherein each additional binary element is adapted toprovide a closed electrical circuit in response to an electrical signalapplied to that element while a liquid level within the compartment isabove that element; and wherein each additional binary element isadapted to provide an open electrical circuit in response to theelectrical signal applied to that element while the liquid level withinthe compartment is below that element.
 3. The ink reservoir of claim 1,wherein each additional binary element is located at a fixed leveldifferent than the fixed level of the first binary element.
 4. The inkreservoir of claim 1, wherein the first binary element is a single-useelement.
 5. The ink reservoir of claim 4, wherein the single-use elementis a fusible link.
 6. The ink reservoir of claim 5, wherein the firstelectrical signal is a periodic pulse having sufficient current andduration to fuse the fusible link if the fusible link is dry and havinginsufficient current and duration to fuse the fusible link if thefusible link is immersed in the ink.
 7. The ink reservoir of claim 5,wherein the first electrical signal is a continuous signal havingsufficient current to fuse the fusible link if the fusible link is dryand having insufficient current to fuse the fusible link if the fusiblelink is immersed in the ink.
 8. The ink reservoir of claim 1, whereinthe first binary element is a multi-use element.
 9. The ink reservoir ofclaim 8, wherein the multi-use element is a bimetal switch.
 10. The inkreservoir of claim 9, wherein the first electrical signal is a periodicpulse having sufficient current and duration to open the bimetal switchif the bimetal switch is dry and having insufficient current andduration to open the bimetal switch if the bimetal switch is immersed inthe ink.
 11. The ink reservoir of claim 9, wherein the first electricalsignal is a continuous signal having sufficient current to open thebimetal switch if the bimetal switch is dry and having insufficientcurrent to open the bimetal switch if the bimetal switch is immersed inthe ink.
 12. A method of determining ink level in an ink reservoir,comprising: applying an electrical signal to the ink reservoir;supplying the electrical signal to a binary element within the inkreservoir; checking for a closed electrical circuit through the binaryelement; determining that the ink level is above a predetermined levelif a closed circuit is detected; and determining that the ink level isat or below the predetermined level if an open circuit is detected. 13.The method of claim 12, wherein applying an electrical signal furthercomprises applying a periodic electrical pulse.
 14. The method of claim12, wherein applying an electrical signal further comprises applying acontinuous electrical signal.
 15. The method of claim 12, whereinsupplying the electrical signal to a binary element within the inkreservoir further comprises supplying the same electrical signal to morethan one binary element.
 16. The method of claim 12, wherein checkingfor a closed electrical circuit through the binary element furthercomprises checking a return signal for a match to the applied signal.17. The method of claim 12, wherein checking for a closed electricalcircuit through the binary element further comprises checking a currentof a return signal against an expected current.
 18. The method of claim12, wherein checking for a closed electrical circuit through the binaryelement further comprises checking a current draw or a voltage drop ofthe applied signal.
 19. A method of determining ink level in an inkreservoir, comprising: applying a first electrical signal to a firstbinary element contained in the ink reservoir; detecting whether anelectrical path is provided through the first binary element;determining that the ink level is above a level of the first binaryelement if an electrical path is detected; and determining that the inklevel is below the level of the first binary element if an open circuitis detected.
 20. The method of claim 19, wherein applying a firstelectrical signal further comprises applying either a periodicelectrical pulse or a continuous electrical signal.
 21. The method ofclaim 19, further comprising: applying a second electrical signal to asecond binary element contained in the ink reservoir; detecting whetheran electrical path is provided through the second binary element;determining that the ink level is above a level of the second binaryelement if an electrical path is detected through the second binaryelement; and determining that the ink level is below the level of thesecond binary element if an open circuit is detected through the secondbinary element.
 22. The method of claim 21, wherein applying the firstelectrical signal and the second electrical signal occur substantiallyconcurrently.
 23. The method of claim 21, further comprising:discontinuing applying the first electrical signal after an open circuitis detected with the first binary element.
 24. An ink reservoir for usein a printing system, comprising: means for containing ink; means forproviding an electrical path through the means for containing ink; andwherein the means for providing an electrical path is adapted to presentan open circuit in response to an electrical signal having apredetermined current and duration applied to the means for providing anelectrical path if the means for providing an electrical path is locatedabove a level of the ink during application of the electrical signal.25. The ink reservoir of claim 24, wherein the means for providing anelectrical path includes means for restoring the electrical path afterpresenting an open circuit.
 26. An ink reservoir for use in a printingsystem, comprising: a body for containing ink; a plurality of electricalcontacts on the body for communication with the printing system; aprinthead integral to the body for dispensing ink, the printheadresponsive to control signals received from the printing system at afirst portion of the plurality of electrical contacts; a first binaryelement contained at a fixed level within the body and having an inputcoupled to a first electrical contact of a second portion of theplurality of electrical contacts and an output coupled to a secondelectrical contact of the second portion of the plurality of electricalcontacts; wherein the first binary element is adapted to provide aclosed electrical circuit in response to a first electrical signal ofpredetermined current and duration applied to the first electricalcontact while an ink level within the body is above the first binaryelement; and wherein the first binary element is adapted to provide anopen electrical circuit in response to the first electrical signal ofpredetermined current and duration applied to the first electricalcontact while the ink level within the body is below the first binaryelement.
 27. The ink reservoir of claim 26, further comprising: a secondbinary element contained at a fixed level within the body and having aninput coupled to a third electrical contact of the second portion of theplurality of electrical contacts and an output coupled to the secondelectrical contact of the second portion of the plurality of electricalcontacts; wherein the second binary element is adapted to provide aclosed electrical circuit in response to a second electrical signal ofpredetermined current and duration applied to the third electricalcontact while an ink level within the body is above the second binaryelement; and wherein the second binary element is adapted to provide anopen electrical circuit in response to the second electrical signal ofpredetermined current and duration applied to the third electricalcontact while the ink level within the body is below the second binaryelement.
 28. The ink reservoir of claim 26, further comprising: a secondbinary element contained at a fixed level within the body and having aninput coupled to a third electrical contact of the second portion of theplurality of electrical contacts and an output coupled to fourthelectrical contact of the second portion of the plurality of electricalcontacts; wherein the second binary element is adapted to provide aclosed electrical circuit in response to a second electrical signal ofpredetermined current and duration applied to the third electricalcontact while an ink level within the body is above the second binaryelement; and wherein the second binary element is adapted to provide anopen electrical circuit in response to the second electrical signal ofpredetermined current and duration applied to the third electricalcontact while the ink level within the body is below the second binaryelement.